Meriwether Lewis did not have any kind of gold in mind, of course, when he toured the valley of the river he called Maria's, and he certainly could not have imagined that beneath its questionable soil lay vast pools of wealth, a black bonanza--petroleum.
The market for petroleum products in America and Europe emerged during the 1850s, when crude oil was first distilled into kerosene to become the favored lamp fuel, replacing sooty animal fats such as whale oil. Natural seeps from oil shale were discovered at several sites in Montana in the 1860s, and an oil boom within the present boundaries of Glacier National Park had a short life between 1890 and 1910. With the advent of the automobile after 1900, the demand for gasoline and lubricating oil expanded proportionately, and so did exploration. In 1910, the Great Northern Railroad began converting some of its coal-burning locomotives to oil, which encouraged further efforts in northern and northwestern Montana.
A few wildcatters brought in a little oil, but nothing commercially viable, and onlookers temporarily concluded that the real gold in "Triangle Country" was on top of the ground, not under it.
The first major oil discovery in Montana was made north of Shelby in 1922. Called the Kevin-Sunburst Field, it was the state's most prolific producer until 1934, when the Cut Bank Field was opened. Prosperity saw the upper Marias country through the Great Depression, peaked in the 1960s, and has been in a steady decline since then.
Black Gold - Oil